Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in e.g., disk form, such as utilized in computer-related applications, comprises a non-magnetic substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (A1)-based alloy such as aluminum-magnesium (Al--Mg), having at least one major surface on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate (deposition) surface, a plating layer, e.g., of amorphous nickel-phosphorus (Ni--P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Cr--V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of carbon (C) or carbon doped with a non-metal element, e.g., hydrogen (H), nitrogen (N), or fluorine (F). A similar situation exists with magnetooptical (MO) media, wherein a layer stack is formed which comprises a reflective layer, typically of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE--TM) alloy layers, one or more dielectric layers, and a protective overcoat layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
According to conventional automated manufacturing methodology, a number of the layers constituting the layer stack are deposited by cathode sputtering, typically by means of multi-cathode and/or multi-chamber sputtering apparatus, wherein a separate cathode comprising a selected target material is positioned in a separate process chamber (which may be located in a larger chamber or form one of a plurality of interconnected process chambers) dedicated for deposition of each layer. According to such conventional technology, media substrates, e.g., disks, are serially transported, in linear or circular fashion depending upon the physical configuration of the apparatus, from one process chamber to another for sputter deposition of a selected layer thereon, the sputter deposition commencing only when the disk has fully entered the respective process chamber in its transit from a preceding process chamber and is at rest. Stated differently, sputter deposition commences and continues for a predetermined interval only when the substrates are not in motion, i.e., deposition occurs onto static substrates.
While such conventional processing, i.e., "static deposition" is satisfactory for sputter deposition utilizing a variety of target materials, e.g., single metal elements, a problem arises when relatively small-sized metal alloy targets composed of two or more metal elements having different atomic masses are utilized for deposition of alloy films or layers on relatively large-sized substrates, e.g., disks. More specifically, since the angular distributions of the metal atoms sputtered from metal alloy targets are dependent upon the atomic masses of the various constituent metal elements of the alloy (A. Weucher et al., J Vac. Sci. Technol. A, Vol. 6, pp. 2316-2318 (1988); L. Zheng et al., J Vac. Sci. Technol. A, Vol. 15, pp. 2431-2433 (1997); P. J. Rudeck et al., J. Vac. Sci. Technol. A, Vol. 7, pp. 2289-2293 (1989)), a substantial (i.e., non-trivial) variation of alloy composition across the deposition surface of a relatively large-sized substrate can occur when the differences in atomic masses of the several component metal elements of the alloy are large and the target is relatively small-sized. In practice, problems associated with non-uniformity of sputtered metal alloy films due to such differences in angular distributions of sputtered atoms become significant when certain metal alloys utilized as the magnetic recording layer in the manufacture of magnetic or MO recording media contain metal elements of very different atomic masses, e.g., cobaltchromium-platinum-tantalum (Co--Cr--Pt--Ta) quaternary alloys, wherein the respective atomic masses of the constituent elements are approximately 60, 52, 195, and 181, and sputtering occurs from relatively small targets onto relatively large and static substrates, e.g., large diameter disks, according to the conventional automated manufacturing processing and methodology, as described supra. More specifically, and with reference to the graphs of FIGS. 1 and 2, the variation in the amounts of Co, Cr, Ta, and Pt contained in sputtered CoCrTaPt magnetic films, when measured across the width of a disk surface from the inner diameter (ID) to the outer diameter (OD) thereof is sufficient to cause a large variation in coercivity and attendant loss in data storage capability.
Accordingly, there exists a need for improved means and methodology for depositing, as by sputtering techniques, metal alloy films and layers having high compositional uniformity across a substrate surface. More specifically, there exists a need for improved means and methodology for sputtering highly compositionally uniform magnetic and other metal alloy layers for use in the manufacture of single and/or dual-sided magnetic and/or magneto-optical (MO) data/information storage and retrieval media, e.g., in the form of disks, which means and methodology provide rapid, simple, and cost-effective formation of such media.
The present invention addresses and solves compositional and uniformity problems attendant upon sputtering of metal alloy targets composed of two or more metal elements of different atomic masses utilized, inter alia, in the manufacture of high recording density, thin film magnetic and/or MO recording media, while maintaining full compatibility with all aspects of conventional automated manufacturing technology. Further, the means and methodology provided by the present invention enjoy diverse utility in the manufacture of various devices and articles requiring metal alloy coating or film layers.